Cover stock is the heavier grade of paper that covers the soft-cover books youâ€(tm)ll find on any bookshelf. Nearly all soft-covered books use 10 pt. C1S. The "10 pt." refers to the thickness of the paper, and the "C1S" merely means "Coated on One Side" with some type of protection, like a glossy varnish.
This is usually a heavier stock paper for the outside 4 pages of your project, (i.e., the cover of a book) providing that it is different from the text (inside pages). If the cover and the inside pages of your project are on the same paper it is called "self cover".
A term used by paper manufacturers for a heavy paper that is suitable for catalogs and other folders. Cover stock can come in "coated" which has a smooth surface, or "uncoated" in its original rough surface.